1. Field of the Invention
The present invention relates to an image pickup apparatus, a non-transitory computer-readable medium storing a computer program, and an image pickup method, for obtaining an image corresponding to a proper exposure time longer than a frame period by synthesizing images.
2. Description of the Related Art
In recent years, image pickup speed of image pickup devices has been increased, and photographing at a high-speed frame rate has become possible while maintaining the number of pixels. The high-speed frame rate provides such advantages that movement of an object in a moving image/live view becomes smooth and the number of sequential photographing frames is increased. However, as the speed of frame rate is increased, the exposure time of one frame becomes shorter. Therefore, in order to obtain exposure time longer than a frame period, the frame rate has to be decreased. For example, when a moving image is photographed at a frame rate of 60 fps, if the proper exposure time becomes longer than 1/60 seconds, the frame rate has to be decreased to 30 fps.
Incidentally, some recent cameras are provided with a function of synthesizing a long time exposure image (hereinafter, shortly referred to as long exposure image, as needed) and a short time exposure image (hereinafter, shortly referred to as short exposure image, as needed), to generate an image having a wide dynamic range (HDR image). Such HDR processing has been performed not only on a still image but also on a moving image or live view image.
In addition to a method of obtaining a long exposure image and a short exposure image alternately for each frame, there is a method of simultaneously obtaining a long exposure image and a short exposure image in one exposure period. In recent years, an image pickup device (also referred to HDR sensor) provided with a function for enabling the latter method has been proposed.
Specifically, the image pickup device called HDR sensor obtains a long exposure image from even-numbered lines and a short exposure image from odd-numbered lines by setting a different exposure time for each line or for each pixel, for example.
In addition, Japanese Patent Application Laid-Open Publication No. 2015-12490, for example, discloses a technique for generating an HDR image without decreasing resolution and frame rate by interchanging the lines for long time exposure and the lines for short time exposure, for each frame.
On the other hand, Japanese Patent Application Laid-Open Publication No. 2007-281548 discloses a technique for generating an image corresponding to a desired exposure time without decreasing the frame rate, by dividing one frame into short time intervals to obtain time-division images and synthesizing an arbitrary number of continuous time-division images, for example.